The present invention relates to a multi-piece solid golf ball. More particularly, it relates to a multi-piece solid golf ball having good shot feel, excellent durability and excellent flight performance.
In commercially available golf balls, there are solid golf balls such as two-piece golf balls, three-piece golf balls and the like, and thread wound golf balls. Recently, the two-piece golf ball and three-piece golf ball having improved flight distance over conventional thread wound balls while maintaining soft and good shot feel at the time of hitting as good as the conventional thread wound golf ball, generally occupy the greater part of the golf ball market. Multi-piece golf balls represented by the three-piece golf ball have good shot feel while maintaining excellent flight performance, because they can vary the hardness distribution, when compared with the two-piece golf ball.
The multi-piece solid golf balls are obtained by inserting an intermediate layer between the core and the cover layer constituting the two-piece solid golf ball and have been described in Japanese Patent Kokai Publication Nos. 332247/1996, 10357/1997, 10358/1997, 313643/1997, 305114/1998, 114094/1999 and Japanese Patent Nos. 2570587 and 2658811. In the golf balls, it has been attempted to compromise the balance of flight performance and shot feel at the time of hitting by using thermoplastic resin, such as thermoplastic elastomer (for example, polyurethane-based thermoplastic elastomer), ionomer resin or mixtures thereof, for the intermediate layer, to adjust a hardness, hardness distribution, deformation amount, specific gravity, elastic modulus and the like of the core, inner cover (intermediate layer) and cover to proper ranges.
In Japanese Patent Kokai Publication No. 332247/1996, a three-piece solid golf ball which comprises a two-layer structured core composed of an inner core and outer core, and a cover is described. The inner core has a diameter of 25 to 37 mm and a center hardness in JIS-C hardness of 60 to 85, a hardness difference from the center point to the surface of the inner core is not more than 4, the outer core has a surface hardness in JIS-C hardness of 75 to 90, and the cover has a flexural modulus of 1,200 to 3,600 kg/cm2. In the golf ball, the inner core (intermediate layer) is formed from rubber composition, and durability is not sufficiently obtained.
In Japanese Patent Kokai Publication No. 10357/1997, a golf ball which comprises a core, and a two-layer structured cover composed of an inner cover and outer cover, is described. The inner cover is formed from ionomer resin and has a Shore D hardness of not more than about 65, the outer cover is formed from ionomer resin and has a Shore D hardness of at least about 60, which is higher than that of the inner cover, and the total thickness of the inner cover and outer cover is at least 0.090 inch (2.286 cm). In the golf ball, the core hardness is not optimized, and rebound characteristics and durability are not sufficiently obtained.
In Japanese Patent Kokai Publication No. 10358/1997, a three-piece solid golf ball of which an intermediate layer is placed between a center core and a cover is described. The intermediate layer has a Shore D hardness of 30 to 55, and the cover has a Shore D hardness of 45 to 58. In the golf ball, the core hardness is not optimized and the intermediate layer is mainly formed from thermoplastic elastomer, and rebound characteristics are not sufficiently obtained.
In Japanese Patent Kokai Publication No. 313643/1997, a three-piece solid golf ball of which an intermediate layer is placed between a core and a cover is described. The core has a center hardness in JIS-C hardness of not more than 75 and has a surface hardness in JIS-C hardness of not more than 85, the surface hardness is higher than the center hardness by 5 to 25, a hardness of the intermediate layer is higher than the surface hardness of the core by less than 10, and a hardness of the cover is higher than the hardness of the intermediate layer. In the golf ball, the hardness difference of the core is large, and rebound characteristics and durability are not sufficiently obtained.
In Japanese Patent Kokai Publication No. 305114/1998, a golf ball of which an intermediate layer is placed between a solid core and a cover, of which the surface of the cover has many dimples, is described. The core has a surface hardness in Shore D hardness of not more than 48, the intermediate layer has a hardness in Shore D hardness of 53 to 60 and the hardness of the intermediate layer is higher than the surface hardness of the core by not less than 8, the cover has a hardness in Shore D hardness of 55 to 65 and the hardness of the cover is higher than that of the intermediate layer, the dimples are consisted of two types having different diameter and/or depth from each other, the total number of the dimples is within the range of 370 to 450, the dimples cover at least 63% of the ball surface, and the index Dst of the overall dimple surface area is at least 4. In the golf ball, the hardness of the intermediate layer is high, and good shot feel is not sufficiently obtained.
In Japanese Patent Kokai Publication No. 114094/1999, a multi-piece solid golf ball which comprises a solid core, and a two-layer structured cover composed of an inner cover and outer cover, is described. The solid core has a deformation amount of 3 to 7 mm when applying a load of 100 kg, the inner cover has a Shore D hardness of 25 to 58 and a thickness of 0.5 to 1.4 mm, the outer cover has a Shore D hardness of 30 to 62 and a thickness of 1.2 to 2.3 mm, and a ratio of the thickness of the outer cover to that of the inner cover is within the range of 1.1 to 4.6. In the golf ball, the solid core hardness is not optimized, and rebound characteristics and durability are not sufficiently obtained.
In Japanese Patent No. 2570587, a multi-piece solid golf ball which comprises a multi-layer structured solid core composed of an inner core and at least one layer of outer core, and a cover is described. The outer core has a Shore D hardness of 30 to 50 and is mainly formed from a mixture of 100 to 50% by weight of polyether ester type thermoplastic elastomer having a glass transition temperature of not more than xe2x88x9225xc2x0 C. as determined by differential thermal analysis (DSC); and
0 to 50% by weight of ethylene-(meth)acrylate copolymer ionomer having a flexural modulus of 200 to 400 MPa; and the cover is formed from ethylene-(meth)acrylate copolymer ionomer having a flexural modulus of 200 to 450 MPa and a Shore D hardness of 55 to 68. In the golf ball, the inner core hardness is not optimized, and rebound characteristics and durability are not sufficiently obtained. In addition, rebound characteristics of the outer core (intermediate layer) are not sufficiently obtained.
In Japanese Patent No. 2658811, a three-piece solid golf ball of which an intermediate layer is placed between a center core and a cover is described. The center core has a diameter of not less than 26 mm, a specific gravity of less than 1.4 and a JIS-C hardness of not more than 80, the intermediate layer has a thickness of not less than 1 mm, a specific gravity of less than 1.2 and a JIS-C hardness of less than 80, and the cover has a thickness of 1 to 3 mm and a JIS-C hardness of not less than 85. In the golf ball, the center core hardness is not optimized, and rebound characteristics and durability are not sufficiently obtained. In addition, rebound characteristics of the intermediate layer are not sufficiently obtained.
In the golf balls described above, sufficient performances has not been obtained in view of the balance of the flight performance and shot feel, and durability at a level of practical use, as described above. Therefore, a golf ball, of which the shot feel, flight performance, and durability are further improved, has been required.
A main object of the present invention is to provide a multi-piece solid golf ball, of which flight performance and shot feel at the time of hitting are improved while maintaining excellent durability.
According to the present invention, the object described above has been accomplished by adjusting a hardness distribution of the core, a hardness of the inner cover and hardness distribution between each layer in the golf ball and the contiguous layer to specified ranges, thereby providing a multi-piece solid golf ball, of which flight performance and shot feel at the time of hitting are improved while maintaining excellent durability.